<template>
   <ul class="list">
        <li class="item" v-for="item of letters" 
            :key="item" @click="handleLetterClick" 
            @touchstart.prevent="handleTouchStart"
            @touchmove="handleTouchMove"
            @touchend="handleTouchEnd"
            :ref="item"
        >{{item}}</li>
   </ul>
</template>

<script>
    
    export default{
        name:"CityAlphabet",
        props:{
            cites:Object
        },
        methods:{
            handleLetterClick(e){
                this.$emit("change",e.target.innerText);
            },
            handleTouchStart(){
                this.touchStatus=true;
            },
            handleTouchMove(e){
                if(this.touchStatus){
                    if(this.timer){
                        clearTimeout(this.timer);
                    }
                    this.timer=setTimeout(()=>{
                        const touchY=e.touches[0].clientY-79;
                        const index=Math.floor((touchY-this.startY)/20);
                        if(index>=0&&index<this.letters.length){
                            this.$emit('change',this.letters[index]);
                        }
                    },12)
                }
            },
            handleTouchEnd(){
                this.touchStatus=false;
            }
        },
        data(){
            return {
                touchStatus:false,
                startY:0,
                timer:null
            }
        },
        computed:{
            letters(){
                const letters=[];
                for(let i in this.cites){
                    letters.push(i);
                }
                return letters;
            }
        },
        updated(){
            this.startY=this.$refs['A'][0].offsetTop;
        }
    }
</script>

<style lang="stylus" scoped>
    @import "~styles/varibles.styl"
    .list 
        display:flex
        flex-direction:column
        justify-content:center
        position:absolute
        top:1.58rem
        right:0
        bottom:0
        width:.4rem
        font-size:12px
        .item
            text-align:center
            line-height:.4rem
            color:$bgColor


</style>